Heretofore widely known in the art is a technique of using a carrier of non-ground magnesium chloride or magnesium alkoxide for olefin polymerization catalysts in homopolymerizing or copolymerizing ethylene or propylene, and this is for improving the catalyst activity and for improving the powder morphology of polymers produced. For example, known are a method of holding a magnesium compound on an inorganic oxide such as silica, for improving the morphology including the particle size and the particle shape of the polymers produced in the presence of it (e.g., Japanese Patent Laid-Open No. 280707/1988); and a method of once dissolving a magnesium compound in a solvent of alcohol or the like followed by re-precipitating it, and using it in producing olefin polymers (e.g., Japanese Patent Laid-Open No. 811/1981). However, the methods are problematic in that their steps are extremely complicated since they indispensably require the step of holding a magnesium compound on a carrier or the step of dissolving a magnesium compound followed by re-precipitating it, and that the properties of the catalysts produced are not stable. On the other hand, another method has been developed, which comprises reacting metal magnesium with alcohol and a specific amount of halogen to prepare a magnesium compound for carrier (e.g., Japanese Patent Laid-Open No. 130107/1992). However, this is still problematic in that the powder morphology (a bulk density, a particle size distribution or the like) of the polymers produced in the presence of it is not all the time satisfactory.
The present invention has been made in consideration of the matters noted above, and its object is to provide a magnesium compound effective in producing olefin polymers having an increased bulk density and a narrowed particle size distribution, not lowering the stereospecificity of the polymers produced and not lowering the polymerization activity in producing the polymers, and also to provide an olefin polymerization catalyst comprising the compound and a method for producing such olefin polymers.